1. Field of the Invention
The present invention relates to a liquid crystal display servable as a projection display, a view finder, a head mount display, and the like. In particular, the present invention relates to a liquid crystal display capable of providing high-quality images by conducting interpolation to correct a nonlinear, uneven light intensity distribution caused by uneven liquid crystal alignment, irregular film thickness, and the like.
2. Description of Related Art
Generally, a liquid crystal display (hereinafter referred to as LCD) has a problem of causing an uneven light intensity distribution over a display screen due to an uneven alignment of liquid crystals or irregular film thickness.
To correct the problem, an LCD according to a related art shown in FIG. 1 employs a gamma correction unit 301, a weight shading correction unit 302, and a modulation shading correction unit 303.
Corrections made by these correction units of the related art will be explained in connection with an LCD display screen 20 shown in FIGS. 8 and 9.
FIG. 8 shows the display screen 20 of an LCD 100. A horizontal side of the display screen 20 is regularly divided into “M−1” sections, and a vertical side thereof into “N−1” sections. In the example of FIG. 8, each side of the display screen 20 is divided into ten sections. Each point that defines a divided section is referred to as a pixel division point P(m, n).
In the example of FIG. 8 where the display screen 20 is divided into ten sections in each of the horizontal and vertical directions, there are 121 pixel division points from P(1, 1) to P(11, 11). In this case, “m” in P(m, n) is defined as 1 ≦m≦(M−1), and “n” as 1≦n≦(N−1).
FIG. 9 is an enlarged view showing a part 20a of FIG. 8. In FIG. 9, a pixel on the display screen 20 is represented as G(x, y) by employing x- and y-coordinates on the display screen 20. A pixel G(x, y) is surrounded by four pixel division points P(m, n), P(m+1, n), P(m, n+1), and P(m+1, n+1). These four pixel division points surround a plurality of pixels including G(x, y), G(x−1, y), G(x+1, y+1), and the like. When the display screen 20 contains X pixels in the horizontal direction and Y pixels in the vertical direction, the variables x and y in G(x, y) are defined as 1≦x≦X, and 1≦y≦Y.
<Gamma Correction>
In the related art of FIG. 1, a first correction to be made is a gamma correction. An image signal S(x, y) for a pixel (x, y) on the display screen is supplied to the gamma correction unit 301. Generally, an LCD has a problem of causing an error if a light modulation ratio (V-T characteristic) is nonlinear relative to a voltage applied to liquid crystals in accordance with an image signal. Although not shown in FIG. 1, the gamma correction unit 301 stores gradation correction values to conduct a gradation correction against such a light modulation ratio error due to V-T characteristics. By using the gradation correction values, the gamma correction unit 301 corrects an error related to a nonlinear light modulation ratio and provides an output signal SG(x, y) to the weight shading correction unit 302.
<Weight Shading Correction>
The weight shading correction unit 302 carries out a weight shading correction to correct differences in the threshold voltages of liquid crystals contained in display pixels caused by uneven alignment of liquid crystals in a liquid crystal alignment film, irregular film thickness, and the like.
The weight shading correction unit 302 has a memory (not shown) to beforehand store threshold voltage difference correction values for the pixel division points, respectively. Namely, the unit 302 stores threshold voltage difference correction values STC_P(m, n), STC_P(m+1, n), STC_P(m, n+1), and STC_P(m+1, n+1) for the pixel division points P(m, n), P(m+1, n), P(m, n+1), and P(m+1, n+1), respectively. With the use of these correction values, the unit 302 carries out the weight shading correction by executing the below-mentioned expressions (1) and (2) in parallel and then the below-mentioned expressions (3) and (4) sequentially and provides an output signal SS(x, y). The signal SS(x, y) is supplied to the modulation shading correction unit 303.
                                                                        STC1                ⁡                                  (                                      x                    ,                    y                                    )                                            =                            ⁢                                                STC_P                  ⁢                                      (                                          m                      ,                      n                                        )                                                  +                                  {                                                            STC_P                      ⁢                                              (                                                                              m                            +                            1                                                    ,                          n                                                )                                                              -                                                                                                                                                          ⁢                                  STC_P                  ⁢                                      (                                          m                      ,                      n                                        )                                                  }                            *                                                (                                      x                    -                    m                                    )                                /                                  {                                      x                    /                                          (                                              m                        -                        1                                            )                                                        }                                                                                        (        1        )                                                                                    STC1                ⁡                                  (                                      x                    ,                                          y                      +                      1                                                        )                                            =                            ⁢                                                STC_P                  ⁢                                      (                                          m                      ,                                              n                        +                        1                                                              )                                                  +                                  {                                                            STC_P                      ⁢                                              (                                                                              m                            +                            1                                                    ,                                                      n                            +                            1                                                                          )                                                              -                                                                                                                                                          ⁢                                  STC_P                  ⁢                                      (                                          m                      ,                                              n                        +                        1                                                              )                                                  }                            *                                                (                                      x                    -                    m                                    )                                /                                  {                                      x                    /                                          (                                              m                        -                        1                                            )                                                        }                                                                                        (        2        )                                                                                    STC2                ⁡                                  (                                      x                    ,                    y                                    )                                            =                            ⁢                                                STC1                  ⁡                                      (                                          x                      ,                      y                                        )                                                  +                                  {                                                            STC1                      ⁡                                              (                                                  x                          ,                                                      y                            +                            1                                                                          )                                                              -                                                                                                                                                          ⁢                                  STC1                  ⁡                                      (                                          x                      ,                      y                                        )                                                  }                            *                                                (                                      y                    -                    n                                    )                                /                                  {                                      y                    /                                          (                                              n                        -                        1                                            )                                                        }                                                                                        (        3        )                                          SS          ⁡                      (                          x              ,              y                        )                          =                              STC2            ⁡                          (                              x                ,                y                            )                                +                      SG            ⁡                          (                              x                ,                y                            )                                                          (        4        )            <Modulation Shading Correction>
The modulation shading correction unit 303 carries out a modulation shading correction to correct differences in light modulation among the liquid crystals of the display pixels caused by uneven alignment of liquid crystals in the liquid crystal alignment film, irregular film thickness, and the like.
The modulation shading correction unit 303 has a memory (not shown) to store light modulation difference correction values for the pixel division points, respectively. Namely, light modulation difference correction values DYN_P(m, n), DYN_P(m+1, n), DYN_P(m, n+1), and DYN_P(m+1, n+1) are stored for the pixel division points P(m, n), P(m+1, n), P(m, n+1), and P(m+1, n+1), respectively.
With the use of the stored correction values, the modulation shading correction unit 303 executes the below-mentioned expressions (5) and (6) in parallel and then the expression (7). Thereafter, the unit 303 employs the signal SS(x, y) provided by the weight shading correction unit 302 to carry out the modulation shading correction by executing the below-mentioned expression (8) and provides an output signal SD(x, y).
                                                                        DYN1                ⁡                                  (                                      x                    ,                    y                                    )                                            =                            ⁢                                                DYN_P                  ⁢                                      (                                          m                      ,                      n                                        )                                                  +                                  {                                                            DYN_P                      ⁢                                              (                                                                              m                            +                            1                                                    ,                          n                                                )                                                              -                                                                                                                                                          ⁢                                  DYN_P                  ⁢                                      (                                          m                      ,                      n                                        )                                                  }                            *                                                (                                      x                    -                    m                                    )                                /                                  {                                      x                    /                                          (                                              m                        -                        1                                            )                                                        }                                                                                        (        5        )                                                                                    DYN1                ⁡                                  (                                      x                    ,                                          y                      +                      1                                                        )                                            =                            ⁢                                                DYN_P                  ⁢                                      (                                          m                      ,                                              n                        +                        1                                                              )                                                  +                                  {                                                            DYN_P                      ⁢                                              (                                                                              m                            +                            1                                                    ,                                                      n                            +                            1                                                                          )                                                              -                                                                                                                                                          ⁢                                  DYN_P                  ⁢                                      (                                          m                      ,                                              n                        +                        1                                                              )                                                  }                            *                                                (                                      x                    -                    m                                    )                                /                                  {                                      x                    /                                          (                                              m                        -                        1                                            )                                                        }                                                                                        (        6        )                                                                                    DYN2                ⁡                                  (                                      x                    ,                    y                                    )                                            =                            ⁢                                                DYN1                  ⁡                                      (                                          x                      ,                      y                                        )                                                  +                                  {                                                            DYN1                      ⁡                                              (                                                  x                          ,                                                      y                            +                            1                                                                          )                                                              -                                                                                                                                                          ⁢                                  DYN1                  ⁡                                      (                                          x                      ,                      y                                        )                                                  }                            *                                                (                                      y                    -                    n                                    )                                /                                  {                                      y                    /                                          (                                              n                        -                        1                                            )                                                        }                                                                                        (        7        )                                          SD          ⁡                      (                          x              ,              y                        )                          =                              DYN2            ⁡                          (                              x                ,                y                            )                                *                      SS            ⁡                          (                              x                ,                y                            )                                                          (        8        )            
The output signal SD(x, y) from the modulation shading correction unit 303 is converted into a display image signal A(x, y), which is subjected to a level conversion to provide a liquid crystal drive signal level. As a result, a display image signal V(x, y) is supplied to the corresponding pixel to display an image.
The processes mentioned above usually employ LUTs (lookup tables) that receive memory addresses and provide corresponding data.
In this way, the LCD of the related art of FIG. 1 employs the gamma correction unit 301 to correct a V-T characteristic error according to the gradation correction values stored in advance.
The gradation correction values according to the related art are prepared without considering pixel positions and are used to correct errors caused by uneven liquid crystal alignment in an original alignment film and interference fringes caused by light made incident to liquid crystals and uneven film thickness. Namely, the related art is insufficient to correct errors caused by uneven liquid crystal alignment and irregular film thickness.
Japanese Unexamined Patent Application Publication No. Hei-7-325308 discloses a technique of controlling spacer detachment to improve image quality, and Japanese Unexamined Patent Application Publication No. 2000-206544 discloses a technique of improving image quality by controlling contamination of liquid crystals due to contaminants contained in a sealing agent. These techniques, however, do not suggest a technique of correcting image signals according to a display screen.